The corrosion of metal equipment by petroleum products is controlled by limiting the corrosivity of the product. In practice, either the level of certain impurities is specified or the degree of corrosion of a specific metal which is allowable under standardized test conditions is specified. The Copper Strip Corrosion Test is such an example. Copper is chosen because it is the most corrosion sensitive metal to be encountered by most petroleum products. In many cases sulfur containing species such as hydrogen sulfide, mercaptans, organic sulfides, carbonyl sulfide and even elemental sulfur are of prime concern.
In the case of the Copper Strip Corrosion Test for liquefied petroleum gas (LPG), a freshly polished piece of copper is immersed in a sealed pressure bomb containing 100 ml of LPG for 1 hour at 38.degree. C. After removal the copper is inspected visually for any tarnish and compared to a standard color chart available from the ASTM. Depending on the degree of tarnish, the LPG is then assigned a grade ranging from 1 to 4, the former indicating essentially no tarnish, and the latter indicating severe tarnish (essentially black). In most situations only grade 1 LPG is used commercially. The exact specifications for this test can be found in ASTM test designation No. D 1838-84. Similar test specifications are available from the ASTM for other products such as Jet fuel, for example.
The test is clearly laborious, time consuming, imprecise and dependent upon an operators visual judgment. Furthermore, the scientific reasons for the formation of the colors listed in the ASTM specification have not been explained before.
It is the purpose of this invention to provide for a method and an instrument to automate and help quantify the Copper Strip Corrosion Test for petroleum products as practiced in a typical refinery laboratory. In addition, it is the purpose of this invention to provide a means for carrying out corrosivity testing on-line as the petroleum product is being produced or shipped via a pipeline, for example.